texts: Do pulsar beams interact with the interstellar medium?

texts:
Pulsars are rotating objects that emit a beam in a direction that is not aligned with the axis of rotation. Because of this, we see them as a periodic pulse. If the beam isn't towards us, we don't see it. Since we need to be on the path of the beam to see it and the beam is only a few degrees wide, it is believed that there are many objects that are pulsars, but that we see as ordinary neutron stars (or can't see at all).

Does the beam from a neutron star interact with the surrounding medium in such a way that we might see the result of this interaction? The same way you can't see a laser beam, but in a very dusty room, you can see the light from the laser bouncing off of the dust particles, making it possible to indirectly see the beam.


texts: Why is Enceladus the only geologically active moon among its neighbours?

texts:
My understanding of why Enceladus is geologically active is that tidal forces from Saturn and - to a lesser extent - from the nearby larger moon Dione provide heat to the moon's interior, just like Jupiter does for Io.

Should the other mid-to-large-sized moons Mimas, Tethys, Dione and Rhea not also exhibit similar activity from the same forces? Granted, Dione and Rhea are further from Saturn and thus less susceptible to tidal stresses, but what about Tethys and Mimas? What special attributes does Enceladus possess that has allowed it to be geologically active in modern times? Is it purely down to the fact that the interior of Enceladus is more ice than rock compared to the other moons, or are there more factors to consider?


texts: Does the Sun have a numerical designation in any star catalogues?

texts:
Given the existence of large star catalogues listing millions of astronomical objects with numerical designations (such as Tabby's Star, KIC 8462852) it occurred to me that one of them might contain the Sun. However, I had no luck.

I searched NASA's HEASARC which combines GRB, SIMBAD, VizieR, NED, and BSC.

HEASARC found Sirius in SIMBAD, NED, and BSC (HR 2491), but there were no results for "Sun" or "Sol".

So, is there any catalogue (maybe a stellar evolution catalogue) that puts the Sun on equal footing with other stars, giving it a canonical number designation?

Bonus high fives if that number is 0 or 1. (Sorry, HR1 is a 6.71 magnitude star in Andromeda, also known as HD 3).


texts: Is a star with 2/3 solar masses and 9/10 solar radii still in the main sequence?

texts:
As far as I know, K-type and G-type stars (among others) grow in radius as they age, eventually leading to red giant phases.
My question is, would a star that is about 0.66 solar masses and 0.94 solar radii simply be an old star still in the main sequence, or would this radius be considered large enough relative to its mass to indicate rapid ballooning into the red giant phase?


texts: Formula to calculate the apparent magnitude of Earth from arbitrary distances

texts: I would like to calculate the apparent magnitude of Earth from various distances, say from the Voyager probe at this moment or from various stars in the sky. I know there must be a formula that I can enter in the distance from Earth (or the Sun) and get out the apparent magnitude. However, I am failing to find it as everything I can find assumes that I am on Earth and want to calculate the brightness of other things.


texts:
The Next Big Future article Rogue Exoplanet 12.7 times bigger than Jupiter is 20 light years away

  SIMP J01365663+0933473 has a magnetic field more than 200 times stronger than Jupiter’s. The object was originally detected in 2016 as one of five brown dwarfs the scientists studied with the VLA to gain new knowledge about magnetic fields and the mechanisms by which some of the coolest such objects can produce strong radio emission. Brown dwarf masses are notoriously difficult to measure, and at the time, the object was thought to be an old and much more massive brown dwarf.

Is this true? Are brown dwarf masses notoriously difficult to measure? Naively, it seems to me if I had brightness at a few wavelengths I could deduce a temperature, and if I had a distance, at least for a blackbody I'd know the area as well.

Are one or both of these in fact difficult to get, or is there something else I'm missing?


texts: Why is a star at its highest point when local sidereal time = RA (right ascension)?

texts:
I'm currently taking a course called Introduction to Astronomy at Coursera. It's not very formal so they didn't present a proof of the statement in the title. I understand why logically one could argue that when a star lies on the projection of the observer's local meridean onto the celestial sphere (I understand that this projection defines the observer's local sidereal time) then this star is at its highest point on the sky.

I haven't found any mathematical proof of this statement and also do not know how to approach the problem geometrically (either euclidean geometry or analytic geometry).

I appreciate any hint or direct answer on how to approach the problem. Thanks.


texts: What is a typical value for core-to-star efficiency?

texts:
I was reading Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds by Kainulainen et al., which discusses star formation rates and efficiencies.

One variable used is $\varepsilon_{\text{core}}$, the core-to-star efficiency, describing how much gas above the critical value of $s$, the logarithmic mean-normalized density, forms a star.

I'm using this parameter in some calculations, but I'd like to use an average value, as opposed to a value for a given molecular cloud.

What is a typical value for $\varepsilon_{\text{core}}$?


texts: The sun is used to determine and measuring time in our solar system. What if we were to travel outside the solar system i.e. to interstellar space, or other galaxies and other celestial bodies (out of our solar system). How would we keep a tab on time then?


texts:
In Duncan and Lorimer's Handbook of Pulsar Astronomy, the equation for the flux density using a radio telescope is given as (for a top-hat function):

$$S=\frac{\beta\,\mathrm{SNR}\, T_{sys}}{G\sqrt{n_{p}\Delta f\,T}}\sqrt{\frac{W_{eq}}{P-W_{eq}}}$$

Here, $\beta$ is a correction factor, $\mathrm{SNR}$ is the signal-to-noise ratio, $T_{sys}$ is the system temperature, $G$ is the telescope gain, $n_{p}$ is the number of polarizations, $\Delta f$ is the observing bandwidth, $T$ is the integration time, $W$ is the equivalent width of the pulse, and $P$ is the period of the pulse.

How does one go from this to the so-called "modified radiometer equation" that is often used (often for an arbitrarily shaped pulse):

$$S=\frac{\beta\,A\, T_{sys}}{G\,N_{bin}\,\sigma_{off}\sqrt{n_{p}\Delta f\,t_{obs}}}$$,

where $A$ is the area under the pulse, $N_{bin}$ is the total number of phase bins in the profile, $\sigma_{off}$ is the RMS of the noise in the pulsar time series, and $t_{obs}$ is the total integration time of each phase bin.


texts: Is Earth's rotation Slowing down or Increasing

texts:
Recently read that Earth is rotating faster than earlier1. However so far it is understood that earth's rotation is slowing down and to conserve the angular momentum Moon is going away from the Earth. What is true?
1for example see answers and comments at What effect does climate change have on the Earth's rotation? in Earth Science SE, and the 2015 Smithsonian article Is Global Warming Changing How Fast the Earth Spins?


texts: Is an expanding universe equivalent to a universe in which everything is shrinking?

texts:
Why do we always think of the universe as expanding?

Surely, from our perspective an expanding universe would look exactly the same as a universe in which everything is shrinking away from everything else? "Oh, but the red shift!" I hear people exclaim. Well how about this:

  The speed of light is simply slowing down.

Hear me out. If the speed of light is a measuring stick against which all things are measured, and if the speed of light is slowing down, then it means everything shrinks and high frequency waves generated in the past are observed with a lower frequency today, which causes us to make observations that the universe is expanding.

What is wrong with my alternative?

Given this, if the speed of light were experiencing, say, exponential decay, wouldn't we expect to see the universe's 'expansion' accelerating? (which I thought was a relatively new and profound discovery)

Apologies if the question is silly, I've never made a formal study of physics and the universe, but this has always baffled me and I haven't been able to find an explanation


texts: Why don't we see the gas behind the black hole?

texts:
In computer simulations of what a black hole might look like and many artist renderings of black holes, they all seem to show the brightly glowing gas BEHIND the black hole due to gravitational lensing.  In all such images (with a "horizonal" accretion disk) this light appears as a thin band on (the "top" or "bottom" of) the event horizon, that appears more and more intense as it gets closer to the event horizon.

But in the recently released image of the black hole in M87, no such lensing effect is visible.  Rather, it looks more like a hazy version of plain ol'Saturnian rings.  Why is that?

This link (http://rantonels.github.io/starless/) contains several images, and some math on what I was expecting to see.  This animated gif of a black hole from various angles, I think, best shows what I was expecting:


texts: What is the size of the universe.is it infinite?

texts: What is the exact size of the universe.is it infinite?


texts: Why do gas giants have clearly delineated surfaces, whereas the Earth's atmosphere fades into space?

texts:
I've just seen this Forbes article.

Why do gas giants appear to have clearly delineated surfaces, whereas the Earth's atmosphere fades into space?

Is it just a matter of scale?  Or is there some form of "surface-tension" for the hydrogen gas?


texts:
I like to think I have a good enough understanding of astrophysics but there's still one thing that I just can't explain.

Why does the Moon orbit the Earth the way it does?

Many other moons in the Solar System orbit their planet along the equator and have a nearly circular orbit. After researching, it seems to boil down to two main causes:

Since every planet rotates on its axis, it has an equatorial bulge, and that extra mass around its equator creates an unequal gravitational field that over millions of years aligns the satellite's orbit around it.
There's a phenomenon called tidal circularization, which on long timescales, acts to dampen the satellite's eccentricity and make its orbit nearly circular.

Okay, that makes sense for most moons. But our own Moon has an orbit that is notably eccentric and it's also inclined to Earth's equator by an amount that somehow changes over time from 18° to 28°. Why is the Moon's orbit so complicated?


texts:
Last night I was experimenting with my mobile phone shooting the night sky adjusting some settings like shutter time and ISO. One of the first pictures I thought was a complete failure, I only adjusted the shutter time to 30 seconds. But when I zoomed in on what I believed to be just some bright stars, I was amazed about what I saw.

Here's the original picture

I zoomed in on the center most bright star and saw this

Then I zoomed in on that star at the bottom just a bit right of the center and saw this.

So I'm wondering what these are? Did I shoot some deep space objects? Or is this just static from the long exposure? Or maybe just pixalating from the zooming? I'm really curious about your answers.

My camera was just pointing at zenit and my location was 50°57'35.5"N 5°05'10.3"E the time was 1:06am on august the 6th 2018.

Here's a screen with some more information about the photo.


texts: Question about the relevant physical parameters to build a backyard observatory

texts:
I live in a big city: São Paulo, Brazil. I would like to build a simple telescope dome to do some amateur sky obseravtions. But the whole project lies on the viability to see something interresting more than just some stars. Due to high luminosity of cities this is a good question to ask.
So, which physical parameters are relevant to decide if a backyard observatory is a good holiday DIY project?


texts: Consequences of strong wind on an alien Planet on the possibility of life

texts:
I was surprised to learn recently that Neptune has winds of 1500 miles an hour.

My question is whether life could ever evolve on such a Planet that has such powerful winds? Not necessarily on Neptune of course but on another exoplanet in another Solar System.


texts:
As a follow-on to my question about seeing Jupiter and Saturn at the same time in my scope, I'd like to ask how I might determine the Field of View (FOV) of my eyepieces. More specifically, I'd like to determine their aFOV (Apparent Field of View?) because that is a configuration setting in Stellarium when you are using ocular view and would like to specify the specs of your eyepiece.
I have two eyepieces that came with my AstroMaster114 telescope. One is 10mm and the other is 20mm. Beyond that, I have no idea what type they are (Plössl? Ortho? Erfle?).
I'd also like to understand how this FOV/aFOV might be impacted by the use of my Celestron #93640 2x Barlow adapter.
Here are pictures of the eyepieces:
Celestron 20mm Erecting Eyepiece

Celestron 10mm eyepiece


texts:
Simple question: I read that the axial tilt of Uranus is 97.77 degrees. I don't understand why it would be this instead of 82.23 degrees the other way. It seems like saying that the Earth's axial tilt is 157 degrees rather than 23, or something. can someone explain why Uranus's axial tilt is bigger than 90 degrees?

EDIT:
this is not a question of how it came to be so tilted, I am sure that is answered elsewhere, but simply why it is accepted as being bigger than 90 degrees rather than less than 90 degrees the other way. it is the same for Venus.


texts: How to calculate how much of the Earth's (or another planet's) surface is visible?

texts:
My latter three questions remain unanswered but I won't wait with this one, I'd like to learn the formula and hope this question gets an answer.
As you're going higher respectively farther away from the Earth, more and more of the Earth's surface is visible. At infinite distance the percentage of the surface that is visible would be 50%. Now I'd like to know how you calculate the percentage that is visible from altitude/distance, and how you calculate the altitude/distance from how much of the surface is visible.
For example, how much of the Earth's surface is visible at 3,000 mi (4,800 km) altitude or at what altitude do you see 38% of the Earth's surface?


texts: What implications do younger Earth and Moon have on Late Heavy Bombardment genesis hypotheses?

texts:
The Late Heavy Bombardment (LHB) or the Lunar Cataclysm is when the inner solar system, including the Earth and the Moon, underwent multiple and sustained heavy impacts early in their history (around 3.7-4 billion years ago). This event formed many of the major impact scars we see on the Moon, (presumably as well as much of the impacts observed on Mars and Mercury). Two main theories are based on perturbations in either the Kuiper Belt, or in a primordial larger asteroid belt.

What implications would a younger Earth and Moon, discussed in "Moon and Earth may be younger than originally thought" (Lars Borg et al., 2011) have on hypotheses on what caused the LHB?


texts: Stellar life cycle flow chart with mass conditions and time scales

texts:
I remember that in my nuclear astrophysics lecture a decade ago, our lecturer drew a large flow chart like diagram of stellar evolution in dependence of the mass of the star (in solar units) on the black-board. I found one from Wikipedia which is close to the one I remember, but less detailed than the one I remember. The content of the linked chart is summarized in my following sketch:

Sadly, neither me nor my former classmates recall which text book or publication the diagram came from, we suspect it was a composition of many sources. The diagram came with a brief explanation of each mass threshold, and it also outlined the governing equations in the respective stellar state. I also remember that there were rough approximates of the time scales of the respective state given.
Maybe somebody can help me out with alternative search terms, references, or a textual answer briefly summarizing the conditions and the state-of-the-art error bars for the mass thresholds and timescales?
Related

The life course for a massive star from birth to death using the HR Diagram and it comments are helpful, but only slightly related
What are the equations governing stellar evolution (Luminosity, Mass, Temperature, Radius) touches one aspect of what I am after
A flowchart from Stephan et al. 2019 outlining the outcomes of binary stellar evolution in the galactic center comes with the right amount of details, but is not for general star evolution.

Edit from 2021-01-22
To make answering easier, I quickly layed out the existing diagram as BPMN which is editable e.g. with this freely available editor. The source code is available via https://pastebin.com/mrafLWa0 - please feel free to reuse, expand and distribution my diagram, just make you comment here where and what for.


texts: Where to find all spectroscopic data about 28 CMa?

texts: I am searching all available spectroscopic data (and particularly wavelength interval) of 28 CMa in the constellation Canis Majoris to measure radial velocities. Which database should I use?


texts: The newly discovered comet NEOWISE has been given the name C/2020 F3. What is the meaning of the F3 and the C in this name?

texts:
The new comet C/2020 F3 was first spotted by NASA's NEOWISE satellite in March 2020.
It is now visible in the NE sky just before dawn. The C may refer to it's non-periodic nature (so far). What does the F3 mean in its name ? The orbit may be parabolic.


texts: Does Big Bang red shift affect the frequency of both light waves and individual photons?

texts: With regard to the wave/particle duality of light, does Big Bang red shift affect both the frequency of light waves, and, the frequency of individual photons? I assume that the e=hf formula relates to individual photons, and not to light waves too?


texts:
I've heard from a lot of sources that Pluto doesn't seem to have any impact craters, but I see a few things that look like impact craters, highlighted in this picture:

For comparison, here's something I think looks like an impact crater on Pluto next to an impact crater on Mercury:

Are they impact craters on Pluto?  If not, what are they?  If they are, why are people saying it has no impact craters?


texts:
The faster you move through space, the slower you move through time - the calculations show that as you approach lightspeed, time comes to a standstill.

How does time work beyond the cosmic event horizon? Space is stretched in every direction, meaning the further away something is, the faster it moves away from us.

But what about when that speed is more than $3 \cdot 10^8 \frac{m}{s}$ due to the distance away from us it is? What happens then?


texts: Is the universe expanding faster than speed of light?

texts: The celestial bodies like stars and galaxies are moving away from each other. How fast are they moving apart? Is that speed more than the speed of light?


texts: Formulas to determine the illuminated phase and orientation of the Moon

texts:
The phase of the Moon (the bright limb) looks different depending on where on Earth the observer is located and the time of the observation. I've located this video and the accompanying spreadsheet that supposedly handles this sort of calculation, however I am somewhat confused on what formulas are actually used. I would greatly appreciate if someone with a bit more experience could decipher the spreadsheet a bit and perhaps write down or link me to the formulas being used.

I'm most interested in determining the illuminated phase (i.e the size of the bright limb) and the apparent orientation of the illuminated portion relative to the horizon. My goal is to understand how this type of calculation is done, in order to re-implement it in code for an application to use - displaying the typical crescent moon icon for night-time, but at the correct angle for a specific location and time.

PS! First post here, so I hope I have used the correct terminology for things.

EDIT: Eventhough the author of the spreadsheet left an answer to the topic, it doesn't feel like it really answers the question. Not to sound clueless and needy, but the question talks about formulas, which I know can be derived from the spreadsheet, however as I have no idea how to approach this, then the answer I was hoping for would help a bit more.


texts: Appropriate battery for overnight viewing to drive telescope and GOTO?

texts:
I have a Plettstone 18" Dobsonian telescope with GOTO and clock drive that runs off a 12 volt cigarette lighter adapter.  What is an appropriate battery to use to run this overnight while viewing all night long and then charge during the day for the following night's use?

In the past I've used deep cycle lead acid batteries, but these are heavy and can fail if not carefully maintained with a float charge.  Also, I don't need cranking power of a car, just sustained energy to drive the scope.  A typical Optima YellowTop deep cycle is rated 75 ampHours.  I don't know what the draw in Amps of my telescope is, but imagine it is less than an amp.

I've also seen these Battery Tender Lithium Iron Phosphate types but wonder if their 10-12 ampHour rating is enough and whether they are meant to be drained over a whole night?  Some say if you get below 8 volts the battery becomes broken, but I doubt the telescope would still run at such a low voltage.

What would a reasonable ampHour rating be?  What kind of battery is a good fit for astronomy equipment overnight?


texts: Will the Earth ever be tidally locked to the Moon?

texts:
From my basic understating,

Momentum is being transfered from the Earth's rotation to the Moon's orbit by tidal friction. The Earth's rotation slows down and the Moon receedes from the Earth as it moves into a higher orbit. This will continue until the Earth's rotational period is equal to the orbital period of the Moon, i.e the Earth is tidally locked to the Moon.

Assuming I have the above correct - and please correct me if I don't - will there, realistically, be enough time for tidal locking to  occur before the sun expands and engulfs the Earth? Or is there another reason the Earth will never be locked towards the Moon?


texts: If the speed at which the universe contracts in reverse time decreases over time, then how did scientists arrive at a date for "The Big Bang"?

texts:
If the speed at which the universe expands is constantly increasing (just like a derivative), then the opposite must also be true: the speed at which the universe contracts in reverse time is constantly decreasing, but, never reaches zero (like an asymptote).

If there is no exact point at which the speed of the contraction of the universe (in reverse time) reaches zero (because an asymptote goes on infinitely), then how did scientists arrive at a "date" for the "big bang"?

Since the speed of the expansion of the universe will go on and on ad infinitum, how can one arrive at a specific beginning point of an infinite function?


texts: Do stars have "radio photospheres"? Are they different from their optical photospheres?

texts:
Comments below What is the maximum distance measurable with parallax? discuss challenges associated with parallax measurements of Betelgeuse and link to Wikipedia’s Betelgeuse; Distance measurements which contains the intriguing paragraph:

In 2008, using the Very Large Array (VLA), produced a radio solution of 5.07±1.10 mas, equaling a distance of 197±45 pc or 643±146 ly.83 As the researcher, Harper, points out: "The revised Hipparcos parallax leads to a larger distance (152±20 pc) than the original; however, the astrometric solution still requires a significant cosmic noise of 2.4 mas. Given these results it is clear that the Hipparcos data still contain systematic errors of unknown origin." Although the radio data also have systematic errors, the Harper solution combines the datasets in the hope of mitigating such errors.83 An updated result from further observations with ALMA and e-Merlin gives a parallax of 4.51±0.8 mas and a distance of 222 (+34/−48) pc.[10] Further observations have resulted in a slightly revised parallax of 4.51±0.80.10
83Harper et al. (2008) A New VLA-Hoppocaros Distance to Betelgeuse and its Implications
10Harper et al. (2017)A Updated 2017 Astrometric Solution for Betelgeuse

When radio astrometry is used to measure positions of Betelgeuse in an effort to determine its parallax, I am guessing (see below) that it is the thermal black body radiation from the star's "radio photosphere" rather than maser radiation from a cloud well outside of the star itself.
(This answer to How far have individual stars been seen by radio telescopes? discusses maser radiation from stars for example)
Harper et al. (2017) contains:

For the purpose of this work, the channels containing line emission were excluded from the analysis and a single continuum data set centered at ≃338 GHz with a ∼5.9 GHz bandwidth was used.

and Harper et al. (2008) mentions:

We have used the highest spatial resolutions available with the VLA, i.e., A-configuration with the Pie Town VLBA antenna, and these allow us to obtain positional uncertainties comparable to Hipparcos. Good u–v coverage was obtained for six frequency bands (Q, K, U, X, C, L)7 at five epochs. For each band we used two 50 MHz continuum channels recording full Stokes polarizations.
7These bands have nominal wavelengths: Q = 0.7 cm, K = 1.3 cm, U = 2.0 cm, X = 3.6 cm, C = 6 cm, and L = 20 cm.

Questions:

Would these then be from the star's "radio photosphere"?
Is there such a thing as a "radio photosphere" that differs substantially from a star's optical photosphere?


texts: Trouble with plotting a graph for the Planck function

texts:
Here is my problem statement:

For a temperature of $7.3 \times 10^5 \ \text{K}$, make a graph of the Plank function (Eq. 3.24), plotting $\log_{10}{\nu} B_\nu(T)$ vs $\log_{10} \nu$ for $\log_{10} \nu$ between 15.5 and 17.5. How does the behaviour of your graph of a blackbody compare with that of Fig. 28.14 for the continuous spectrum of the quasar 3C 273?

Here is the equation 3.24

\begin{equation}
    B_\nu (T) = \frac{2h \nu^3/c^2}{e^{h\nu/kT}-1}.
\end{equation}

I have put together an excel spreadsheet and created a graph of $\log_{10}({\nu} B_\nu(T))$ vs $\log_{10} (\nu)$, however, it is just a straight line (which is what I would have expected although the graph in the book is significantly different). I am wondering if I am misunderstanding the problem statement. What I did to get my data points for $\log_{10}{\nu} B_\nu(T)$ is I first computed $\nu$ values from the given range of $\log_{10} \nu$ values, then I computed B(T) values with the above-given equation. Then I substituted the product into logarithm : $\log_{10}({\nu} B_\nu(T))$, thus obtaining my $y = f(x)$ values. and then I plotted it against  $x = \log_{10} \nu$. Am I doing things wrong or is this fine?


texts: Is the curvature of Mars visible from the top of Olympus Mons?

texts:
Would you be able to see the curvature of Mars from the top of Olympus Mons? And how much curvature would you see if it was visible, would it be only barely detectable, or would you see a lot of curvature?

Olympus Mons is 25km high and the tallest known mountain in the Solar System.

Mars is just over half the size of Earth.

Here on Earth, the curvature of the planet is hardly visible from the height of commerical aeroplane (roughly 10km).  I was wondering, considering the height of Olympus Mons and the size difference of Mars, if the curvature from up there would be very pronounced.


texts: How would the night sky look from inside a globular cluster?

texts:
When the weather is clear, we can look at the stars. And we normally would see several thousands of them, they all being more than a $\textrm{pc}$ away from us.

Now, there are globular clusters, which consist of some $10^5$ stars concentrated is a few $\textrm{pc}$ area. From oustside they look like this:

Now, how do they (and the whole sky) look from inside? Imagine that solar system is inside such a cluster. Would it be a big change? Would there be a significant difference between night and day? Would it be easier or harder to study astronomy there?

P.S. The credits for the question go to Ross Church.


texts: Do we know if there are asteroids leading or following Earth in Earth's orbit around the Sun?

texts:
A search of the Internet is so clouded with discussions about the asteroid belt or asteroids orbiting the planet Earth that I couldn't see an answer to my question.

Do we know if there are asteroids orbiting the Sun in Earth's orbit (NOT orbiting the Earth).

To be clear: these would be asteroids located somewhere around the Sun at the same distance as Earth, either following it or leading it in the Earth's own orbit around the Sun.

I hope that was clear.


texts: If the earth stopped spinning what would happen to the moon

texts:
A question was posed at work today, "if the earth stopped spinning what would happen to the moon"? Ignoring any effects on the Earth, what actually happens to the Moon? Does it continue to orbit the now non-rotating Earth, or does it fly off into space like a massive asteroid, or more likely some other thing that I can't conceive of?

Note, the Earth stops spinning, not orbiting the sun.

For additional curiosity, what would be the differences if this were an extremely gradual slowing vs an almost instantaneous stoppage?


texts: Internet Resource which register all Ultra-long Gamma-Ray Bursts

texts:
I read in a scientific magazine there was new gamma bursts that last longer than usual.

One was detected during december 2010, also known as Christmas Burst: GRB 101225A
and another one in 9th of December 2011, GRB 111209A

They were both detected by the "Swift" program and this article goes into detail.

I do not know if there is another programs for GRB detection and I would be curious to find a resource on Internet which registers/records all Ultra-long Gamma-Ray Bursts on one single page/site (across all research/programs).


texts:
I downloaded fits file using wget script from https://exoplanetarchive.ipac.caltech.edu/docs/datasethelp/ETSS_CoRoT.html
I am not able to view the file. I tried atsromagic and DS9 .  After File->Open I get an error message "..error while reading.." .It happens with both softwares.
Is anyone able to view these files? If yes, which software did you use?
Another possibility is that using using wget script on windows it got corrupted. Is there a command line tool to check integrity/validity of fits file?


texts: Collimating with a home-made collimation cap

texts:
I've made a home-made collimation cap and am trying to use the procedure linked to in another answer.

However, I've run into two issues right off the bat.  In this picture from the linked page, it shows a "primary mirror donut". All I see is a black circle with nothing in between.  I'm using a piece of bright white paper that I printed the alignment patterns on to attach to the eyepiece and I thought this would be bright enough to see, but apparently not.

The second issue is that this method seems to rely on there being four "spider vanes" which are holding the secondary mirror in place.  However, my telescope only has one, making it seemingly impossible to line anything up.

Here is what it looks like through the cap:

It looks like the dark circle in the middle it fairly well aligned, but I can't tell for sure if it needs any adjustment.  And I'm not sure how to deal with the fact that there is nothing inside the circle to align with.  I have tried taking an LED flashlight and shining it on the top of the paper while i look through the pinhole and if I focus the LED circle on the edge of the paper at 90 degree intervals it appears to be aligned, but I don't know if this is sufficient.

Incidentally, the halo around the outside seems to be the edge of part of the inside of the side tube, and it does not move when I adjust the collimation screws.


texts: Could an Applegate-like mechanism operate in AM CVn systems?

texts:
One of the controversies surrounding the detection of exoplanets around post-common envelope binaries is the possibility that the orbital period variations observed might be the result of the Applegate mechanism as opposed to reflex motion from an orbiting planet.

Would these concerns also apply to AM CVn systems or other close white dwarf+white dwarf binaries? The Applegate mechanism itself is explained in terms of the activity cycle of the main sequence component of a cataclysmic variable, could a similar mechanism operate or would the changes in the quadrupole moment of the star be too small to produce observable effects?


texts:
The Earth likely froze over almost completely about 700 million years ago. This increased its albedo significantly, and I wonder if that would have a considerable effect on its apparent magnitude from other planets. (The Sun was like 4% fainter, though.)

If so, would the Earth be naked-eye visible from farther away 700 mya than it is now? Maybe from Uranus's moons?


texts:
I heard our universe is flat. Then one question is puzzling in my mind. If our universe is really flat, why we measure distance from any point across in a spherical way. In other words, why we say, the comoving distance (radius) is now about 46.6 billion light years. If this radius is only treated for observable universe, then how does science find that the universe is flat knowing nothing beyond the limit of the universe.

There are some questions in SO, however, they do not assimilate what I intended to know. In this question, for instance, OP asked about whats the shape of the universe. And also there are some terms related to black holes, 3D shape, ball etc. Apart from those complexity, my intention is simply to be clarified, why we call our universe flat? And by word flat, what I meant "having a level surface; without raised areas or indentations". Am i missing any alrernative meaning of flat here?


texts:
I was out in the garden having a cigarette and was watching the shy looking at three stars for about 5 minutes. suddenly they moved in the sky and crossed paths.one has now stopped still and would just look like a star the other moved right across the sky and has now stopped also. if you were looking at them now u would think they were just a normal star in the sky.
what are they really?

Has someone else seen this before I have seen this about 5 times in the last ten years


texts: What is the maximum number of planets in the habitable zone?

texts:
At present, it seems like we are alone in our solar system. How many earth-like planets would fit into the habitable zone of the solar system?

The orbits should be stable for quite a time, i.e. for life to evolve, let's say 4.6 billion years.
The habitable zone may be estimated from 0.725 to 3.0 astronomical units, according to Wiki.

Could one use perturbation theory to answer this?


texts: What is wrong with my calculations of Venus' orbital period?

texts:
I am trying to use Kepler's second law to find the duration of Venus's orbit. I am assuming circular orbits (using Earth and Venus, so low eccentricity). Here is my process:

Assuming that the radius of Earth's orbit is 150 million km, then the swept area in one day is $\frac{1}{365.25}\times\pi\times 150^2 \approx 194 \text{ million km}^2$.

Venus must sweep the same area in the same time. Assuming a orbital radius of 108 million km for Venus, and using $A = \frac{\theta}{360}\pi r^2$, we can find the central angle for the swept sector, that is, the angle traveled in one Earth day:

$194 = \frac{\theta}{360}\pi \times108^2 \implies \theta = 1.90 ^{\circ}$ per Earth day.

Hence the orbital period should be $\frac{360}{1.90}\approx 189$ Earth days.

Of course, the orbital period of Venus is $224.7$ Earth days. The difference between 189 and 224.7 appears to be well beyond the error introduced by my assumption of circular orbits.

What am I doing wrong?

I know this is perhaps a circuitous way of doing this calculation. My goal is to write a mathematics exercise that uses the area of sectors in a meaningful way.


texts:
Watching this video describing the "next generation" space telescope, it seems like the biggest mirror will be ~6 meters in diameter.
Theoretically, if a telescope was built in space instead of shipping it pre-built, and the mirror was, not a few meters, but a few kilometers, (and whatever other important aspects of a space telescope that a novice like myself has no idea about, multiply them by a few orders of magnitude) would it provide benefits proportional to the size difference?


texts: How much is usually deposited in a Mars regional dust storm?

texts: Is there any indication of how much dust is deposited, especially in areas that are not open where wind might produce a cleaning event?


texts:
There are various modes of Cepheids like

single modes:
   fundamental (F),
   first overtone (1O), and likewise.

And then we have

double modes: F/1O, 1O/2O etc.
triple modes: 1O/2O/3O etc.

What are these modes actually? What do they mean and which frequencies do they correspond to?

Stellar pulsations are caused by expansions and contractions in the outer layers as a star seeks to maintain equilibrium. What kind of equilibrium is being referred to here?


texts: What limits the usable focal length of telescopes currently?

texts: What barriers - of technology, physics and possibly economy (things that would be possible technologically but are simply too expensive) sets the upper bound on quality of telescopes for observation of the sky in visible spectrum - observing surface of distant objects at maximum resolution/detail?


texts: Do NEA (Near Earth Asteroids) have minable water ice?

texts: Water is very useful for rocket fuel and life support in space. But does water, in abundance and form which conceivably could be usefully mined this century, really exist in NEA's? Or do we have to go all the way out to the frost line, the Asteroid Belt, to find asteroids with available water? (Lunar polar water ice is not topic here, I think, but low delta-v asteroidal water).


texts: Calculating the date and year when a lunar eclipse will fall on the Winter Solstice

texts: I am a novelist working on a new book, titled Werewolves In The Christmas City, which happens to be Bethlehem, Pa. In 2010 when I was working on a book titled The Christmas City Vampire, a lunar eclipse on the Winter Solstice occurred. As you know it was the first one since 1638. On the 2010 occurrence, I added the resurrection of two werewolves-twins-turned during that eclipse of 1638. My question is: How would my professor character figure out that the event will occur in 2010. The time frame I am in right now is 1947. I would appreciate any help you can give me. Math is certainly not one of my strong suites.


texts: How long until the Earth and Moon become a binary planet?

texts: With the rate at which the moon is further receding into a higher orbit, how long until the barycentre between us and the moon leaves the earth, and going by the IAUs 2006 definition update, we become a double planet?


texts: How do I know, mathematically rather than from observation, if a moon is full?

texts:
I know about the equations to describe the orbit of a moon around a planet. I know the moon's semi-major axis and eccentricity, and the same for its host world with the star they orbit.

Is there any equation that tells me how much of the moon is illuminated at night, and possibly how bright, as seen from the planet?


texts: Is there evidence for galactic "seasons"?

texts:
The Solar Year has huge effects on our climate, and the signs of passing seasons are physically evident on Earth. I recently learned about the Galactic Year. To my understanding, our sun orbits the Milky Way galactic center about every 200-225 million years. Do we know if there are any "seasonal" changes due to our position in the galaxy? One season of the orbital period (50+ million years) feels like a long enough time to leave a mark, if any effect exists:

in the formation of solar system objects?
the bombardment of planets and moons with meteors?
the number, type, distribution, or trajectory of comets?
the shape or density of the Oort Cloud?
in Earth's geologic record?
(at a stretch) mass extinction events?

Obviously you can just say "gravity affects everything, of course the solar system is influenced to some degree by other objects." But I mean specifically, is there evidence for any cyclical pattern which might be related to our position in the galaxy?


texts:
The current system of constellations is historical and has kind of arbitrary boundaries.

This has a number of obvious downsides:

Difficult to define boundaries need complex tables to express
Each constellation subtends a different solid angle (area of sky)
etc

Has anyone ever proposed, or does anyone use, a system of cutting the sky into regular chunks, that are either simple to define or similar in area?   Do any of these systems (if they exist) attempt to preserve the most important/famous constellations (as least the part people normally see) ?


texts:
It is obvious that the longitude of ascending node ($ \Omega $) of a planet gradually changes with time. For example, the VSOP planetary theory accounts for this. In Astronomical Algorithms (Meeus 1998), one finds for example that, for Mercury, $ \Omega = 48.330893 - 0.1254227 T - 0.00008833 T^2 - 0.000000200 T^3 $ (referred to the standard equinox J2000.0).
While formulas to calculate the precession of the perihelion of a planet are easy to find (e.g., in “Calculation of apsidal precession via perturbation theory” by Barbieri and Talamucci), I am having a hard time finding sets of formulas pertaining to the advance (or regression!) of the ascending node.
Can someone please give me a few references of where I could find them? Thanks in advance!
(Reason: I’d be interested in calculating precise planetary orbits for an imaginary planetary system, or maybe even for known planetary systems such as TRAPPIST-1.)
EDIT: Most of the formulas found online (including those given in answers and comments) are either restricted to the Solar System, or restricted to one body orbiting another one. I’m looking for something that would be in the form of $ \dot \Omega = \sum_{i = 1}^{\infty} k m_i m_0^x $ where $ m_i $ is the mass of the perturbing body, $ m_0 $ is the mass of the perturbed body, and k and x are, well, what I’m looking for! Their determination probably includes G (the constant of gravitation) and R (the distance between the two bodies) and so on…


texts:
My "real question" is in Space Exploration Meta (neo (near-earth-object) and near-earth-asteroid tags, do we need both?), but I think that astronomers will be able to help understand the situation and terminology.

Question: Is there a distinction between NEOs and near-Earth asteroids? Is there a difference? Or is it a distinction without a difference?

I noticed for example that here in Astronomy SE there is just near-earth-object.


texts: Why hasn't the Earth fallen into the sun yet?

texts:
So the Earth's been orbiting the sun in a relatively stable orbit for billions of years now. during that time, it's been plowing through dust, and hit by comets and asteroids, presumably mostly from the outer reaches more than the inner parts of the solar system.

Even if the drag and increased mass should amount to a tiny, tiny fraction of Earth's mass, shouldn't that have been enough to cause our orbit to spiral inwards? Both due to slowing of the Earth's motion, and an increase in mass?

Thanks!


texts: Pluto- Current theories regarding its geological nature?

texts:
The images of New Horizons from Pluto will take more a year to arrive from space, for the moment with have some compressed images as a preview.

Nasa has advanced some information regarding the geologically inactive zone, but there has been no information regarding the possible geologically active zones, on the formation of the plateaus and the mountains.

What forces could be driving geothermal activity of what nature on Pluto? What can be learnt from theories of the moons of Jupiter and Saturn to understand activity inside of Pluto? What is the theoretical temperature of the center of the dwarf planet?


texts: Fresnel lenses for a makeshift Galilei telescope?

texts:
For a kindergarden (pirate) party, friends of me want to build together with the 4 year old kids a functional pirate's telescope for each of the kids. On the web I found full constuction sets, e.g. http://www.astromediashop.co.uk/Telescopes.html (I am not affiliated), but that is only half the fun than improvising and building with household things.
Does anybody has experience building a makeshift telescope using the cardboard tube from a paper kitchen roll, in particular which lenses to use and how to fix them?
The rolls are e.g. 25.5cm long and have an approximate diameter of 4cm. Ideally, we would need two fresnel lenses, I guess, but I am not sure which ones to choose, how to fix them nicely to the tube etc.
Looking forward to your ideas.
Edit: In the meantime, I also found View the Stars Through a DIY Telescope which just states:

[You neeed]: 2 convex lenses (you can get these from a pair of magnifying glasses or by ordering lenses online)

Finding suitable lenses (with right focal length, diameter, weight) is actually the hard part.
Thinking further how I recycle things from home, I got the rough idea to build water lenses but this is clearly out of scope of a kindergarden project, or is it?


texts: Why is the Boomerang Nebula colder than the CMB?

texts: An earlier answer on temperature mentioned that the temp of the Cosmic Microwave Background (CMB) is $2.4\,{\rm K}$ and the temp of the Boomerang nebula as ${\rm 1\,K}$. How did the nebula cool faster than the CMB?


texts: Recently, the most distant object in the solar system was discovered. How was this accomplished?

texts:
It was recently announced that the most distant object in our solar system was discovered. This object averages 132 AU from the sun. The object, initially named Farfarout, was estimated to be 400 km across. How was such a small object found and its orbit estimated by a ground-based telescope? This seems to really be pushing the limits of observable objects. Or am I wrong on this?
Ref: https://phys.org/news/2021-02-astronomers-orbit-distant-solar.html


texts: Difference between "planetary ring" and "circumstellar disk"?

texts:
Related: Do/Can Ringed Stars Exist?

Is there any particular difference, in behavior or properties, between a planetary ring system and a circumstellar disk? Or is the only real difference a matter of what's in the middle?

This question came up as a matter in the related discussion, particularly because the (game-simulated) object that inspired the question is a brown dwarf - something between a star and a gas giant. What I observed in-game appeared to be more similar to the rings around Saturn, than to the description and image provided of a circumstellar disk.

So, are there properties of the rings/disks themselves which can differentiate one type from another? Or is the type of central body the only thing that defines them?

If the central body is the only factor, what should we call a ring around a brown dwarf, assuming one could exist in nature?


texts: Does mean solar time and sidereal time sometimes indicate the same time?

texts:
I'm trying to wrap my head around the different definitions of time. Since mean solar time depends on the Sun, and sidereal time depends on the stars, and since the position of the Sun relative to the stars changes over the course of the year, does this mean that the difference between the two times increases and decreases over the course of the year?

Once a year, mean solar time and sidereal time will be the same. Is that right?


texts: Why do stars born in a cluster finally disperse?

texts: In other words, if a group of stars born within the same nebula, e.g. the Pleiades, are initially gravitationally bound - what causes them to finally get separated and proceed individually? Is it the influence of  "external" mass? Or, are they now and we're they always, even at birth, having the escape velocity? (If the latter is true then I think they should not be considered truly bound from the beginning...)


texts: Can the electromagnetic counterpart of a gravitational be seen by 'small' telescopes?

texts:
As follow-up question for my previous question I'm thinking about the search for the electromagnetic (EM) counterpart of a gravitational wave (GW). Is it possible to search for those events with 'normal' telescope, the ones (professional) amateur astronomers have? What I mean with a (professional) amateur astronomer is: a telescope with an aperture of 10" or more (remote) and the ability to do long exposures.
Is that equipment capable of detecting the EM counterpart of a gravitational wave (in theory)? Thanks in advance!
EDIT: I'm not sure if there is an EM counterpart in the visible light at all. Is this the case? Can such an event, that triggers a detectable GW, been seen in the visible light (by extension: with 'amateur' telescopes as stated above)?


texts: How to calculate eclipses the heliocentric way?

texts:
It is my understanding that modern methods for calculating the time and
location of solar and lunar eclipses (e.g. NASA website
https://eclipse.gsfc.nasa.gov/eclipse.html) are integrating equations of
motions to determine the positions of the Earth, Sun and Moon relative
to each other. The models may include other solar system objects (e.g.
Jupiter) and treat objects not as point-like but extended to improve
accuracy and prediction range into the past and future (several millennia).
This is quite sophisticated, but hard to follow for people
unfamiliar with Newtonian mechanics and numerical methods.
This made me think about a more accessible method to compute eclipses.
If I make less stringent requirements for accuracy, say,

Prediction range: +/- 5 years from today,
Point of maximum eclipse: Within 500km of true location.

Is it then possible to compute positions of Earth/Moon using a
heliocentric model where they move periodically in ellipses, possibly
with apsidal/nodal precession and enough other periodic perturbations to
achieve the desired accuracy? In other words, add a few vectors
parameterized by time to get the positions of the Earth and Moon
in a coordinate system where the Sun is at the origin. (Which CS would be most useful?)
Ideally, one would plug in a reference position/date, some solar system
constants like sidereal year, sidereal day, synodic month, etc,
a date and then get the 2 positions.
(Computing where the shadows intersect the Earth or Moon is not
considered part of this question, just the centers of Earth and Moon.)
I've been researching this for months now and ordered a book on astronomical algorithms, but could not determine whether I'm trying something stupid...


texts: Is the Sun visible from Proxima Centauri to human eyes?

texts: I know that the light coming from Proxima Centauri is not bright enough to make it naked-eye visible from the Earth. Is the Sun naked-eye visible from Proxima Centauri?


texts: The path of the planets on the celestial sphere

texts:
I know that planets have a "wandering" movement on the celestial sphere. I also know that their period around the Sun vary largely as compared with the period of the Earth (one sidereal year), according to Kepler's third Law. I'm also aware though that their translation planes are closely co-planar with the ecliptic.

Hence, there must exist a pattern of their position with respect to the fixed stars on the celestial sphere.

Can someone give some links, rules or charts on how to find out the celestial path of the planets on the celestial sphere over the year(s), with respect to the constellations of fixed stars?


texts: Why do the planets orbit in the same direction?

texts: Theoretically, planets would have an approximately equal chance of going one way in their orbit or another but in reality, this is not the case (at least in our solar system). Why is this?


texts: How do we know how the Sun (or any star, for that matter) will evolve?

texts:
The evolutionary path of the Sun has been described in some detail, and, subtle differences aside, it's been described as such for decades - the Earth-engulfing red giant stage, the helium flash, etc.. It would seem that the knowledge necessary to make such a prediction has been around since the 60s, if not earlier.

How do we know it will happen, and on the timescales described? If we make some measurements/estimations of the mass and composition of the Sun, and use our understanding of nuclear physics - energy of fusion and so forth, and an understanding of Newtonian physics (or do we have to invoke Einstein?), do the predictions just inevitably fall out?

Could the predictions be wrong? Is there any significant measure of uncertainty, perhaps due to sensitivity of certain calculations to initial conditions, etc?

Is the red giant future of our Sun a firm conclusion, or just a likely possibility among a range of others and commonly talked about merely because it seems the most likely one?


texts: Calculating the orientation of the night sky

texts:
How would one calculate the rotation/tilt of the earth to simulate the Night Sky in a self-written tool or app. I am trying to built an app for my telescope to show me on my phone what I am looking at. I can already simulate the exact positions of stars at the 1.1.2000 at 00:00:00 but I dont know how the "earth" should be rotated so I can simulate the sky from my current position and accurate time.

There are App and tools like stellarium that can achive this but I just cant get the angles right:

If anyone could point me in the right direction and tell me what I need to change/calculate it would help me a lot.


texts: where to obtain ephemeris data for geodesy satellites?

texts:
Is anyone aware of where one can obtain ephemeris data in Geocentric Celestial Reference Systems (GCRS) coordinates for a geodesy satellite such as LAGEOS (It doesn't really matter which mission)? Or, alternatively, simulated data in GCRS coordinates. Specifically, Cartesian position and velocity coordinates. I can't seem to find them anywhere.

Update: My confusion has increased. I will try and rephrase my question.

Is it possible to obtain an ephemeris file and perform a transformation such that the ephemeris data can be expressed in GCRS coordinates? And if so, what is the process?

Purpose of question:
What I am interested in is ephemeris data for a satellite (doesn't really matter which mission) that is subject to classical Newtonian acceleration plus relativistic corrections as recommended by the IERS such as Schwarzschild, Lense-Thirring and Geodetic accelerations.


texts: What units are used for the Stefan-Boltzmann law?

texts: I have a star with given temperature in Kelvin and radius in solar radii. I tried to calculate the luminosity of the star using Stefan Boltzmann's law, and got an absurd number (over 1 million). What am I doing wrong, and are there any units that I should use instead of Kelvin and solar units?


texts: Image processing techniques to distinguish between stars and galaxies in an image?

texts:
Say I have an arbitary image of stars and galaxies without any extra information (no other spectra info other than image itself). Can you help me distinguish them?

Are there any specific features / properties I could look for? Say for eg the R G or B value or maybe values in some other color space (YUV etc.) be more or less for stars than galaxies, etc.

EDIT:

I dont have any "special" data (no sensor or spectral data), I only have data from the internet (common images). The point is to detect stars and galaxies from images commonly found on the internet.

One of them is this: https://cdn.spacetelescope.org/archives/images/large/heic0916a.jpg


texts: Finding the solar noon based on longitude and latitude?

texts:
Please could someone advise the best method of finding the solar noon based on location?

http://pveducation.org/pvcdrom/properties-of-sunlight/suns-position

The stuff on here has been helpful but I can't figure out what I should be finding out!
LST sounds about right, but I'm not 100% sure.


texts: Calculating the black hole evaporation time

texts:
Black holes evaporate very, very slowly by emitting Hawking radiation, and eventually they disappear, maybe even during the lifetime of the universe ($\sim 1.5 \times 10^{18}{\rm s}$). That's what I recall from the lectures I attended.
I now stumbled upon a Black Hole Evaporation Time Calculator which uses this formula:
$$\tau_{\rm evaporation} \sim \left( \frac{M_{\rm black~hole}}{M_\odot}\right)^3 \times 10^{66} {\rm ~years}$$
As usual,  $M_\odot$ is the solar mass. My questions: How is that formula deduced? In which limiting case(s) does it hold?
Edit Just as a reminder: Right now, $4.3 \times 10^{17} {\rm s}$ passed since the big bang.


texts: Type I delta-Cepheid star, calculation of apparent maginute and luminosity

texts:
I am curious to see if I have calculated this correctly:

  A Type I delta-Cepheid star with a one month (30day) period is put at the distance of the star Vega.
  a)  Determine the apparent magnitude this star would have.
  b)  Determine how many times more luminous the delta-Cepheid star is compared to Vega.

My workings:

a) Absolute Magnitudes given for Type I delta-Cepheid star:
$$M=-2.8log\left(P\right)-1.43$$

using the information given $P=30$

$$M=-2.8log(30)-1.43=-5.58$$

Absolute magnitude is given by
$$m-M=5log\left(d\right)-5$$

using information for calculate value of $M$ and that vega = $8Pc$

$$m=5log\left(8\right)-5+5.58=5.10$$

b)
Apparent magnitude is given by
$$m_1-m_2=-2.51log(\frac{F_2}{F_1})$$

as the two start are at the same distance then I will be left with just luminosity.

so adapting the above equation and subbing in the required values

$$0-5.10=-2.51log\left(\frac{L_c}{Lv}\right)$$

Rearrange

$$10^{\frac{5.10}{2.51}}=\frac{L_c}{L_v}$$

$$107.61=\frac{L_c}{L_v}$$

so therefore

$$L_c=108L_v$$

where subscript c is delta-Cepheid  and subscript v is vega

Is this calculation correct?


texts: When was the concept of rogue planets first theorized?

texts:
So after watching the Kurzgesagt video about life on rogue planets I became fascinated by the concept. I did some digging, and the earliest reference to the concept I could find was Philip Wylie's When Worlds Collide: a Sci Fi novel written in 1933. In the novel Wylie writes

  A sort of body that they knew existed by the millions, probably, all through the universe-something they were sure must be, but the general existence of which has never been actually proved.

The best I could come up is with after LePlace's nebular formation hypothesis became more widespread in the 19th century people just assumed rogue planets would exist. I certainly can't find anything written about them before Wylie's novel. It doesn't help that the first use of the term 'rogue planet' I could find was George R. R. Martin's novel Dying of the Light and any earlier mentions than that use several different terms to illustrate the concept.

tl;dr Who first theorized the concept of rogue planets and when did they do so?


texts: Whats the name of this eye-shaped galaxy?

texts:
I would like to know the name of this eye-shaped galaxy:

Strange eye-shaped galaxy has black-hole iris, Betsy Mason, 23.07.2009, Wired.com:


texts: Possible to make a cheap reflective objective lens with a mirror?

texts: Sounds kinda crazy and cheap but has anyone ever tried to take a flexible (plastic) mirror and attach a string to the back side then pull the string so it makes a concave surface? I realize it wouldn't be the most accurate device in the world, but if I wanted to build a telescope with a child I think it would be a cheap and fun way to make it. Thoughts?


texts:
What is the exact measurement of a light year? I searched google for the answer in meters and came up with $9.461\cdot 10^{15}$ meters. When I calculated the answer considering $299\,792\,458 \;\text{m/s}$ as the speed of light, I came up with:

$$
299\,792\,458 \times 365 \times 24 \times 3\,600 = 9\,454\,254\,955\,508\,926 \;\text{m}
$$ Why is there such a gap? Did I miss something to add in the equation or is it just wrong?


texts: How to separate binary and optical stellar pairs?

texts:
I have list of stellar pairs from The Washington Double Star Catalog (WDS), i.e. I have next parameters:

angular separations
position angles
stellar magnitudes of both components

Additionally I have GAIA DR2 parallaxes (and other parameters) from SIMBAD database. How to distinguish between binary and optical stellar pairs?


texts: From CMB anisotropy data observed in 1992, did astronomers figure out that the universe should be accelerating before its discovery in 1998?

texts: CMB anisotropy was measured in 1992. I assume that astronomers, then, like now, would have been able to deduce the cosmological constant and things like that from the CMB anisotropy data. Then, from the cosmological constant and things like that, they would have been able to find that the current universe was accelerating. Did they indeed know that the current universe should be accelerating before its observation in 1998? Or, was the discovery in 1998 a great surprise? What was the exact situation between 1992 and 1998?


texts: Coordinate transformations between reference frames in spherical astronomy

texts:
Suppose there are two observational frames of reference with origins $O$ and $O'$, respectively, separated by some constant distance. A body located at point $P$ has Cartesian coordinates $\left(x,y,z\right)$ and $\left(x',y',z',\right)$ in $O$ and $O'$, respectively; and similarly, the spherical coordinates of $P$ in the unprimed and primed frames are $\left(r,\theta,\phi\right)$ and $\left(r',\theta',\phi'\right)$.

Say $O$ determines the Cartesian coordinates of $O'$ to be $\left(a,b,c\right)$. Then the Cartesian coordinates of $P$ in $O$ are simply related to the primed Cartesian coordinates: $$\left(x,y,z\right)=\left(x'+a,y'+b,z'+c\right)$$

My question, then, is how does one compute the affect of translation on spherical coordinates. That is, given $\left(a,b,c\right)$, how can one write $\left(r,\theta,\phi\right)$ as a function of $\left(r',\theta',\phi'\right)?$


texts: 2D Distorted Star Map for Pasting on Sphere Surface

texts:
Are there printable 2D star maps that are distorted such that, when printed, they can be cut (along printed lines) to be applied to the outside of a sphere to represent the celestial sphere, as seen from the center of the substrate sphere?

Is there a term for this type of map?

If they don't exist, how can one be created?


texts: How do I calculate the Hill radius of a star in a binary system?

texts:
Is there an easy way to calculate the Hill radius of a star in a binary system at different orbital radii where both stars are of the same mass and in circular orbit around one another’s centre of mass?

I have seen a formula for calculating Hill radii but it’s meant to address the stability of orbits around a small body which itself orbits a large one, an example of which would be the effect of the Sun's gravity on the orbit of an object around the Earth.

Can the same formula be used if both major bodies are of similar or the same size, for example to address the stability of planetary orbits around one star in a binary system?


texts: What exactly is the "paradox" in Olber's Paradox?

texts:
To the extent of my understanding, Olber’s paradox states that if the universe was static and homogeneous, we should see a star at every point in the night sky and therefore the night sky should be equally as bright as day.

However, since the night sky is dark and non-uniform, it can be said that the universe is not static and not homogeneous. However, if this was already known, what exactly is the “paradox”? Why isn’t it called Olber’s Observation or something else?


texts:
My friend sent me a video of a kind of a halo phenomenon and asked me what kind of halo it is.

There is a 22 degree circular halo around the sun.

But there is also a ring which seems to go horizontally around the entire sky. The ring is the same height as the sun. It seems to start and end where the 22 halo is at the same height as the sun (3 and 9 o'clock on the halo) and goes horizontally around the sky.


texts: Can there be a 2nd possibility deduced from the fact that galaxies are moving away from us?

texts: I just read that according to the BBT the universe is expanding. This is evident from the fact that distant stars (and galaxies) are moving away from us. But it could also happen that the universe is in fact shrinking to a very small point and we being far away from the point are experiencing its pull less than those that are near it. It may be like a race where a very fast (in 1st place) , a moderately fast (in 2nd place) and a slow car (at last) are racing . To the moderately fast car it would seem that the other two are moving away from it,but actually they all are moving towards the same point -the end. So it may happen that earth is like the moderately fast car moving towards the collapse point at a different relative speed. Is this proposition possible? If not,why?


texts: Do free protons and neutrons absorb much radiation? To affect astronomers' observations? If so, at what wavelength(s)?

texts:
In a plasma, or wherever, do the completely ionized nuclei commonly absorb much EM radiation?  Or any free neutrons or protons?  Can astronomers detect this?  Enough so that astronomers take it into account in their observations?
I've read elsewhere that protons, neutrons and nuclei, even when free of any electrons, usually (or only, depending on who you read) aborb and/or emit only hard X-rays and gamma rays...
Is this true?


texts: Would an ultra bright moon indicate that the world is ending?

texts:
There is a sci-fi television episode that shows a man looking out the window into the night sky. There up in the sky is the moon, and it's extraordinarily bright.

The man spends the rest of the night trying to do all the things he wish he had done in his life. A race to experience life before the morning sunrise.

His conclusion; A giant solar flare has erupted, and the side of the Earth facing the sun has been burned away. The world is ending....

How plausible is this story?

Could a solar flare burn the Earth? and if you happen to be on the dark side when it happens. Would the moon be a reliable indicator?


texts:
Stephen Hawking proposed that a black hole emits radiation as it evaporates.

Black holes don't let any radiation escape their event horizon because even particles with the speed of light get trapped by their magnetic field.

Does that mean when black holes emit radiation, they just re-absorb it?


texts: What are the stages in the life of a universe?

texts:
Geological periods describe varying phases in the last few hundred million years on earth.
Are there any names for the periods on a timescale 1-2 orders of magnitude greater, that is, for the stages of a/the universe?
I found some bits and pieces of information but nothing as clear as I did for geological periods, possibly because of the conjecture involved.


texts: Why are planetary orbits not all circular?

texts: Why are the orbits of the planets elliptical ? The circular orbit also satisfies all the conditions of gravitational force. Then why did nature choose the elliptical orbits ?


texts: Where will the planned Deep Space Atomic Clock orbit "after" Earth?

texts:
I've seen multiple sources repeat the information that the Deep Space Atomic Clock will 'at first' orbit Earth, before moving on out of Earth orbit.

  The Deep Space Atomic Clock (DSAC) is a miniaturized, ultra-precise
  mercury-ion atomic clock for precise radio navigation in deep space.
  It is orders of magnitude more stable than existing navigation clocks,
  and has been refined to limit drift of no more than 1 nanosecond in 10
  days.

Wikipedia: "Its development will include a test flight in low-Earth orbit"

JPL: "the instrument will be tested in Earth orbit for one year, with the goal of being ready for future missions to other worlds"

What would it then orbit? The Sun? Or some L point? Other planets? Or will multiple ones orbit all of the above?

Edit: for those wanting to close based on "not astronomy", have you considered astronomy does not have to be done from earth and indeed much of the data astronomers use often comes from probes and satellites in space.  Therefore 'how/where will this space beacon be used?' has strong impact on future of astronomy.


texts: Does this amateur observation hold a record even including robotic searches for supernovae?

texts:
The new paper in Nature A surge of light at the birth of a supernova (doi:10.1038/nature25151) describes the fortuitous capture of a supernova "Shock Breakout" - the earliest rise in brightness of a supernova only about 4 hours old. An open access epdf is linked in the Washington Post article if you click from inside it: A self-taught astronomer spotted something no scientist had ever seen which is a good read itself.

  His discovery, reported Wednesday in the journal Nature, is a landmark for astronomy. Buso’s images are the first to capture the brief “shock breakout” phase of a supernova, when a wave of energy rolls from a star’s core to its exterior just before the star explodes. Computer models had suggested the existence of this phase, but no one had witnessed it.

Is this the earliest that such a phenomenon has been "seen" by a person, or does this observation also hold the record after including all of the automated searches for supernovae by robotic telescopes as well?

below: "Astronomer Victor Buso poses in front of the telescope with which he witnessed the birth of the supernova 2016gkg. (Victor Buso)" From here. Click/open for full size.


texts: How is the incidence angle of the Sun related to the lean angle of the Cooks pines?

texts:
Auracaria columnaris (Cooks pine) on average lean towards the equator.  Most of the pines in the Northern Hemisphere lean southward and most of the pines in the Southern Hemisphere lean northward.

The above picture is from Johns et al. 2017, who performed a study of 256 Cooks pines across 18 regions on 5 continents.  Though they don't publish their data set in the paper, we can see that the leaning effect is more pronounced for the higher latitudes.

At higher latitudes, the apparent location of the Sun in the sky becomes more biased in the opposite direction.  For example, in far Northern Alaska, the Sun mostly appears in the Southern half of the sky.  Could phototropism be an explanation for the Cooks pine lean? Does the North/South component of the Sun's average incident angle by latitude match the above table?
Question: Consider a perfect blackbody disk elevated slightly from the ground.  For a given latitude $L$ what is angle $\theta$ between a fixed disk and the local tangent plane that maximizes yearly absorbed wattage from the Sun (assume no horizon obscura).


texts: I witnessed a steady stream of falling stars slowly falling one after another this morning. What was it?

texts: This morning at 6:18am I witnessed a steady stream of falling stars that lasted at least 90 seconds from the time I noticed it. I live on a farm east of Edmonton, Alberta, Canada and the stars were falling from the south to the east and fading as they neared the tree tops. They fell at 70 degrees east. Any idea what it is I witnessed?


texts: How does this strategy for chasing the sunset work?

texts:
In Randall Munroe's What If? blog he tackles this question:

  What is the longest possible sunset you can experience while driving, assuming we are obeying the speed limit and driving on paved roads?

His final answer is the following, which allows you to experience about a 95 minute sunset. But the diagram isn't the most self-evident. What does the diagram mean, and how does the strategy work?

  If you're in northern Norway on a day when the Sun just barely sets and then rises again, the terminator (day-night line) moves across the land in this pattern:

  To get a long sunset, the strategy is simple: Wait for the date when the terminator will just barely reach your position. Sit in your car until the terminator reaches you, drive north to stay a little ahead of it for as long as you can (depending on the local road layout), then u-turn and drive back south fast enough that you can get past it to the safety of darkness.


texts: Gaia Gbp - Grp: why does it get larger as star gets redder?

texts:
As an enthusiastic amateur scientist, I'm plowing my way through a cool Gaia DR2-based paper, "An Empirical Measurement of the Initial-Final Mass Relation with Gaia White Dwarfs". I'm doing all right, but have hit a roadblock: understanding the meaning of the stellar color value GBP - GRP.

GBP is the blue photometry value, and GRP is the red photometry value, so GBP - GRP is the difference between the two, giving a number broadly encoding the star's color. Here's a graph from the paper that uses this value:

It's a graph of white dwarf ("WD") color versus absolute magnitude. On the left, the absolute magnitude MG increases (downwards) as the star grows dimmer, and across the bottom the color GBP - GRP increases (rightwards) as the star grows redder. Hence the slope of the curve; as a WD cools, it gets smoothly dimmer and redder.

But wait! as a star gets redder, the the "blue" brightness should become relatively smaller than the "red" brightness, right? So, the GBP - GRP value should get smaller and smaller, right? But that's the opposite of what this graph (and other graphs in the paper) apparently shows.

Should GBP - GRP get larger as a star cools and gets redder? Where am I confused? (I'm assuming the professionals aren't all confused...)


texts: Why is gravity only an attractive force?

texts:
As per the universal law of attraction, any two bodies (having some mass) experience a force of 'attraction' which is proportionate to ...and ...inverse proportionate ....

Then comes my question: Why it should be force should be of type 'attraction' only ?  Why it should not be repulsion / any other kind of force ?


texts: In an area with lots of light pollution, which clear sky clock parameter is most important?

texts:
I live on the periphery of a large light dome, looking towards the West. I get about 1/3 of the sky towards mountains that is darker. According to ClearDarkSky.com I live in an area with artificial to night sky brightness ratio of about 9.00, Sky Brightness mags / arcsec2 V Band of about 19.5, and Bortle Scale of about 5.

On the Clear Sky Clock (also at ClearDarkSky.com) I see the following sky values:

Cloud Cover
Transparence
Seeing
Darkness

Which of these values is most important in a light polluted area, especially when looking west in my case to the darker sky portion?  I'm thinking it is transparency as low transparency may result in more scattering of light pollution and thus more pollution?  But perhaps moon phase beyond a certain portion matters too, especially if the moon is in the west.

I have a large Dobsonian telescope and wonder which of these is going to have the most beneficial effect when viewing near the city?


texts: If a rocky world is large enough (not a gas or ice giant) can it have helium from the primordial disk in its atmosphere?

texts:
When planets are formed do only gas and ice giants accrete hydrogen and helium? Does this accretion have to be beyond the "snow line"?

In other words, would all hydrogen or helium in the atmosphere of a super-earth come from outgassing (radioactive decay, etc)?


texts: Where does the dust on 67P/Churyumov-Gerasimenko come from?

texts:
As we (laymen) are told, comets lose gas and dust when they descent into the denser regions of the solar system. Seemingly so much and so large parts that they can even cause meteor showers like in the case of the Leonids from 55P/Temple-Tuttle.
Nevertheless we were also told, that the surface of 67P is covered with several centimeres of dust over a much harder surface. Where does the dust come from? The solar wind should have blown away any lose dust long ago, no? Is there a process which regenerates dust on the surface every cycle?


texts:
This question is somewhat related to my earlier question How are the compositional components of exoplanet atmospheres differentiated?, but this about a specific surface-atmospheric phenomena - volcanism.

Using our solar system as a rough analogue (where asides from Earth, Venus, Io and Triton have active volcanism, probably more), volcanism should be not uncommon amongst exoplanets given the right conditions.  Obviously, we could probably only detect either the massive shield, plateau volcanism, or prolonged volcanism from multiple vents.

What observational constraints are there in detecting the presence of volcanism on exoplanets?


texts: Are there any simulations of the Grand tack?

texts:
The BBC program with Brian Cox "The Planets" involved some description of the Grand Tack hypothesis to explain the current state of the solar system.

This theory has Jupiter wandering through the solar system causing various orbital disruptions. Are there any computer simulations/CGI videos available to show how Jupiter may have achieved this? On a sightly unrelated note: I recall reading Velikovsky's "Worlds in collision" many years ago. He had a similar idea but attempted to attribute these changes to biblical events / comets. He was many orders of magnitudes out in terms of timing and the size of the disruption, but I suppose he could be credited with hinting that Geological uniformitarianism might not be applicable to the solar system.


texts: How are neutrinos produced in blazar jets?

texts: I was watching the press release about measuring neutrinos and gamma rays from a distant blazar. One of the presenters mentioned that the neutrinos are associated with very high energy protons caught up in the jet produced by the galactic nucleus. What I don't understand is what interation(s) is producing the neutrinos in this scenario. What sort of particles must the protons be interacting with to produce these neutrinos?


texts: What calculations show that Comet Shoemaker-Levy 9 orbited Jupiter for several decades before its spectacular impact? (Chodas, Sekanina & Yeomans)

texts:
This answer to A moon in eccentric orbit dipping below Roche limit includes the following about Comet Shoemaker–Levy 9

Here is a nice figure of its last passes:

I looked up "fragment A" in JPL's Horizons and it provides a modeled trajectory only between 1992-07-15 and 1994-07-17 but the link cited above says

Computations by Paul Chodas, Zdenek Sekanina, and Don Yeomans, suggest that the comet has been orbiting Jupiter for 20 years or more, but these backward extrapolations of motion are highly uncertain. See "elements." and "ephemeris." at SEDS.LPL.Arizona.EDU in /pub/astro/SL9/info for more information.

If I paste some of that into a search engine I get http://spider.seds.org/sl9-list.html with lots and lots of links, but now I'm in way over my head.
Question: What calculations show that Comet Shoemaker–Levy 9 was orbiting Jupiter for several decades before its spectacular impact? (Chodas, Sekanina & Yeomans) Where can I read about these calculations? Have there been further refinements since, based on any subsequently discovered historical precovery data?


texts:
According to general relativity, would gravitational waves experience the same sort of redshift that electromagnetic waves experience due to the expansion of the universe?

And are there astrophysical processes that would be expected to have a characteristic 'frequency signature' analogous to the lyman or balmer series of hydrogen which would enable a measurement gravitational wave redshift.

I'm thinking of processes like baryon accoustic oscillations, certain types of supernovae, neutron star mergers, etc.


texts: Why does moon moves to side if I change my position directly into it?

texts: I've setup this scenario on Stellarium where the moon is aligned with East direction. I wanted to see the change of altitude of the moon if I move straight into its direction (time of observation is always the same) but instead it keeps changing its direction to the left. I expected to keep on the same azimuth and only change altitude but no, and I don't understand the geometric reason of it, for example If I walk in a straight line towards a building it won't move right or left. On the equator works as I expected.


texts: Are there clouds/clusters of gas in space that have red and blue color adjescent to one another?

texts:
In artistic renditions of space scenes, there were stunning depictions of gasses or galaxies with bold red and blue colors immediately adjacent to one another, in contact as water is with oil in a container. I wonder, are there known arrangements of gas like that, with both ends of the color spectrum adjacent to one another? If so, what are some examples, what is known about them, and what causes the two colors?

One reason I'd call it into question is that I'd imagine the properties of boldly blue gasses are different than those of red gasses. Maybe that assumption is wrong because the property of color isn't necessarily associated with other properties. Another assumption would be that gasses with very different properties wouldn't find themselves collecting adjacent to one another in space. That assumption could also be wrong - I'm not an astronomer and only have basic understanding of physics and chemistry.


texts: How does gravity affect pressure under water?

texts: How different would being under water in Europa differ from being under water on Earth? Would it be possible to dive deeper on Europa with a submarine than on Earth and by how much?


texts: How do you carry errors for brightness magnitudes

texts:
I have a value for the relative flux $F_2/F_1$. With some uncertainty value $a$.
If I use the equation to get relative magnitude: $m_1 - m_2 = 2.5 \log_{10}(F_2/F_1)$
How do you now calculate the uncertainty value $a$ for this equation? Do you just do the same equation but applied to the uncertainty value or is there some other alteration you have to make to uncertainty values?


texts: Does Eddington's variable polytropic index better fit data from the Standard Solar Model?

texts:
I came across a 1938 paper by Arthur Eddington1 in which he discusses stellar polytropic models where the polytropic index $n$ varies inside the star, decreasing from a value $n_2$ at the surface to a value $n_1$ at the center. He specifically mentions that the case of $n_1=1.5$ and $n_2=3.5$ should represent "ordinary gaseous stars" quite well.

In his conclusion, he states

  We have seen that actual stars are likely to be represented by a model with $n$ continually increasing outwards.

78 years later, we have better data about the structure of the Sun, thanks in part to helioseismology. So I have two questions:

Do researchers use Eddington's variable index treatment in theoretical models?
Does Eddington's model better fit current data from the Sun than the standard polytropic model with $n$ constant throughout the star?

I ask partly because I know that the standard polytropic model (with $n=3$) begins to fail in the outer regions of a star, thanks in part to convection, as shown below, and I wondered if even a simple two-phase model could suitably describe a convective envelope.

Graphs from this page.

1 Eddington mentions earlier work by Milne (1932), who uses a slightly more complex analysis. I haven't yet read Milne's paper, so I'm not familiar with its conclusions and use.


texts: What zodiac constellation will the Vernal Equinox be directed towards in ~6500?

texts: My question is basically asking how the vernal equinox changes with time, and how we can track where it will be at certain points in time.


texts: What if we throw two solid objects parallel in space? Do those two objects have any chance to collide with each other?

texts:
What will happen if just throw two solid objects (for example, solid footballs) parallel in outer space and those two objects are floating and going far away in the universe.

So is there any possibility in which those two football-size solid objects can collide with each other, or will they will float parallel for an infinite amount of time in the universe?

I'm considering gravity also, and I find that other stars's and planets's
gravitational pull can pull them into their gravitational fields and change their direction.

But what if those two objects will never get destroyed by luck? Could those will collide each other?


texts: Faster Earth spinning speed to overcome gravity, possible?

texts:
As far as I know we stick to the surface of the Earth as its gravity is pulling us and Earth rotation is in a way reducing the gravity.

At what speed should Earth be spinning so that we all get ejected / catapulted into space (if we all line up on the equator).

Sub question: at what speed of spinning would we all “stick” a few meters above the ground?


texts: Would I actually be able to see Ceres without shining a really bright torch onto it?

texts:
NASA's put out a semi-CGI video of a Ceres flyby using material from the Dawn mission.

Now I realise that visibility is relative, even on Earth: I can walk into my basement and not be able to see anything until I've stood there for a few moments letting my eyes adjust. But I'm wondering, since Ceres is so far from Earth, and despite the images we see beamed back from spacecraft, if I were on a spacecraft in orbit of Ceres, facing the side of Ceres that faces the Sun, would I be able to see its surface with the naked eye? Or is sunlight too dim at that distance to do the job on its own?


texts:
The following image is a map of the area surrounding the Local Bubble. One side of the image is 1700 lightyears. From the Sun to the Hyades (immediately below the sun) it is 150 lightyears.
The local bubble, with the sun in its center, has three immediate neighboring bubbles, numbered in roman numerals, Loop I, II, and III. At the lower right edge we can see a section of the Orion-Eridanus-Superbubble.
What is the name of the area marked in green?

Image source: Henbest/Couper, The Guide to the Galaxy. Found online at http://www.astronomy.ohio-state.edu/~pogge/TeachRes/Ast162/ISM/Local500pcAnn.gif


texts: What is the largest recorded solar flare?

texts: For the purposes of this question I would interpret the word "recorded" as loosely as possible meaning that historic records such as ice cores or tree rings would count. Also what effect did such a large flare have on life on Earth at the time?


texts: Existence of a mass-volume astronomical chart?

texts:
I've been wanting to make a mass-volume (or mass-radius) chart for astronomical objects ranging from asteroids to supermassive black holes on a log-log scale. A sort of 'Hertzsprung-Russel' type diagram but with mass and volume as the axes.

I wanted to check first to see if anyone else has done this before. Google doesn't seem to turn up anything of the sort, and so I'm wondering if anybody in the esteemed audience of Astronomy.SE would know of the existence of such a diagram.


texts: Can cosmic rays alone produce noticeable aurorae in bodies far away from the Sun?

texts:
Aurorae are caused by energetic particles interacting with planetary atmospheres. Part of this flux comes from the Sun (solar wind) while the rest is cosmic radiation. My main question is: could a planetary body located far away from the Sun (or any other star), with a suitable atmosphere and magnetosphere, have noticeable* aurorae, just from being exposed to cosmic rays? A related question would be: do we know how much of the aurora is caused by the solar wind, and how much by cosmic rays? And thirdly: is there any other way that a planetary body could produce aurorae, such as its own electromagnetic emissions?

*I know "noticeable" doesn't really work as a limit, but for the time being, I'm talking of electromagnetic radiation that can be distinguished clearly from the background of a planet's disc using instruments not more advanced than our current telescopes at interplanetary distances.


texts:
I understood that everything was made of Atoms.

  An atom is the smallest constituent unit of ordinary matter that has
  the properties of a chemical element. Every solid, liquid, gas, and
  plasma is composed of neutral or ionized atoms

However with Neutron Stars;

  the basic models for these objects imply that neutron stars
  are composed almost entirely of neutrons, which are subatomic
  particles

Does this mean neutrons can exist outside of an atom, and that a Neutron star isn’t comprised of an element that is recognisable on the periodic table?


texts: Is it possible that only one hemisphere of a planet has an atmosphere?

texts:
Suppose there is a tidally locked planet orbiting a star. The planet's surface consists of a global ocean, that is, liquid water. At the inner hemisphere the temperature is so high that the water is constantly boiling, creating the atmosphere of water vapor. But the vapor does not reach the dark side of the planet, and precipitates around the terminator line. The further side has no atmosphere and an icy surface.

Is this setup possible? Can it be such thing that one side of a planet has liquid (and boiling) water surface while the other side has no atmosphere?

Is it possible at all that a part of an ocean was boiling while the other one was icy?


texts: When Betelgeuse goes supernova, will the explosion hit any neighboring stars?

texts:
There is evidence Betelgeuse might go supernova "soon". Are there any stars in the vicinity of Betelgeuse that are close enough that they will be hit by the explosion of this supernova? What would be the effect on stars near Betelgeuse?

A supernova "kicks" out the other star if it is in a binary pair, but Betelgeuse is not a binary, so this doesn't quite answer the question.


texts: How to project galaxy data in x y z coordinates?

texts:
For a data visualization project, I want to extract galaxy data (in x y z coordinates) from galaxy catalogue of within 150 mpc and project each of those galaxies as dots and visualize them in a 2D projection of a spherical volume. Need your help in getting this data set and how to achieve it?

Would be grateful for any help in any way!


texts:
This is a question I've heard many times in the past, and a quick search of the site says it hasn't been asked here, so I figured I might as well ask (and answer) it. I know that it is rare for someone to ask and answer their own question, but I think it could work here, and I welcome input (including other answers) from anyone and everyone here.

The Sun is roughly 4 light-years away from the closest star system, the Alpha Centauri system. The planets in our Solar System, however, aren't even close to that far away from the Sun. Where does our Solar System end? Is the edge considered to be the orbit of Neptune, the Kuiper Belt, the Oort Cloud, or something else?

Note: this question on Physics SE is similar, but the answers posted here go in different directions.


texts: Is there a timekeeping word for the orbit of a moon?

texts:
For a planet, we can colloquially refer to its period of rotation as a "day" and its period of revolution around its parent star as a "year." Some worlds have unique terms, such as Martian days being referred to as "sols", but the principle is the same: one word for rotation around its axis, another for revolutions around the star.

Is there an equivalent word for the period of a moon's revolution around a planet? On Earth it roughly lines up with a "month," but multi-moon planets would have different periods for each moon.

If I was in charge of timekeeping for a mission to Europa or Ganymede, what term would I use to refer to the period of time it takes for the moon to complete one orbit of Jupiter?


texts: Conversion between Astronomical Frames, ex. IRCF, FK5, FK4, etc…

texts:
I'm a little bit confused about reference frames, and I was wondering if someone could help clarify a few things?

So let's say I have equatorial coordinates that refer to the mean equator and equinox of an non standard arbitrary epoch. Now, if those coordinates are referred to the mean equator and equinox that epoch, then is the mean equator/equinox of the specific epoch considered the reference frame for those coordinates?

…and then how would you go about converting those coordinates to another reference frame like say the IRCF or FK5? I assume that I would need to precess them to J2000 accounting for any applicable proper motion (and if they referred to the true equator nutation). What else do you need to put them in either the ICRF or FK5 frames?

Also, something else I'm confused about is the epoch of a reference frame. So, let's say I have the IRCF astrometric coordinates of a planet at JD 2456963.5 TDB (or any other arbitrary date). Since they're IRCF coordinates, then the epoch of the reference frame is still J2000, but the coordinates refer to the instant of 2456963.5 TDB correct?

Any clarification would be greatly appreciated, and thanks in advance!


texts: Why is sun's photosphere a million times less dense than air at the surface of the Earth?

texts:
Sun's photosphere is about 19 times as hot as Earth's surface.
(Source: http://solar-center.stanford.edu/vitalstats.html)

But Solar surface gravity is about 28 times terrestrial surface gravity.

So, shouldn't the density of gases at the photosphere of the sun be comparable to that on the surface of the Earth?

Why is the density of Sun's photosphere a million times lesser?
(Source: http://solar-center.stanford.edu/vitalstats.html)

Essentially, what I am asking has been aptly worded in userLTK's answer, "how can the photosphere be so light and almost vacuum like under such high gravity (28 earth gravity)"?

Some of the answers have suggested that this may be because the Sun's photosphere is ionised. This doesn't seem to be accurate. The Hydrogen ionisation at optical depth = 1 is only 0.04%.
(Source: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1968SoPh....3....5G&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf)


texts: Stellarium script for sunrise times affected by topography

texts:
I customised my own landscape with stellarium, created my own horizon with the polyline setting like horizon_Geneve.txt file.
Manually, I can increase/decrease time to see when the sun's upper limb  touches the horizon, so my question is:
Is there a possibility or a script, to make the mission automatically, for many days instead to test each day then note it?


texts: Do most planetary systems have fewer planets than the solar system?

texts: It is my impression that most planetary systems have, at most, three to four planets. Is that real? Or is it just that we lack the ability to detect most planets?


texts: What programming languages does SETI (Search for ExtraTerrestrial Intelligences) most commonly use for signal processing?

texts: Please give preference to those most widely used in the field, if possible.


texts: When will a day on Earth & Mars be the same length?

texts:
I read on Wikipedia that:

  As on Earth, the period of rotation of Mars (the length of its day) is slowing down. However, this effect is three orders of magnitude smaller than on Earth because the gravitational effect of Phobos is negligible and the effect is mainly due to the Sun.[19] On Earth, the gravitational influence of the Moon has a much greater effect. Eventually, in the far future, the length of a day on Earth will equal and then exceed the length of a day on Mars.

So, how far into the future exactly will it be when the length of a day on Earth and Mars will be equal? Also, for how long will their day lengths be within say, one second of each other?

By "day", I mean the Mean Solar Day.


texts: Is there a way to calculate the mass of of a stellar remnant given the initial mass of the star?

texts:
Assume there is a star in a completely empty region of space, away from any outside influence.
Is there a way to calculate the mass of a resulting stellar remnant, a white dwarf, neutron star, or black hole(variations is accuracy are completely fine) that will result after a star dies, only given the star's mass around the time in which will die? (like an equation or something)
And, is there a way to calculate the resulting remnant's mass only given the star's initial mass during its formation?
It would be appreciated if one were to provide a concrete method or graph for determining such.
Thanks in advance!


texts:
I want to back-predict solar eclipses as part of a research project.
My main goal is to obtain a list of all solar eclipses that took place over a tight grid (let's say of 100km by 100km) for the years 5000BC to 4000BC (just as an example).

Ideally, I'd like results to follow, more or less, the format here of https://eclipse.gsfc.nasa.gov/JSEX/JSEX-SA.html, but any library you can suggest will be fine.
According to the previous reference, "The Besselian elements and values of ΔT used in Solar Eclipse Explorer are the same as those used by Five Millennium Canon of Solar Eclipses: -1999 to +3000. For the purposes of calculating eclipse circumstances from a given place, the growing uncertainty in the value of ΔT and the corresponding longitude become unacceptably large outside time period of -1499 to 3000 (1500 BCE to 3000 CE)." and hence I could not use their tool.

Since I will simply count how many eclipses could be seen at the center of each square on my grid for the 1000-year period, I can tolerate large inaccuracies in the timing of eclipses. Moreover, as long as errors are random, I can also afford missing some eclipses or having them missplaced.

Is there any resource I could use to compute eclipses as I described?